Peripheral Component Interconnect Express (PCIe) is a computer expansion card standard designed to replace older PCI, PCI-X, and AGP bus standards. Recent revisions of the PCIe standard support hardware I/O virtualization. PCIe is based on point-to-point topology, with separate serial links connecting every device to the root complex (host). A PCIe bus link supports full-duplex communication between any two endpoints, with no limitation on concurrent access across multiple endpoints. PCIe communications are encapsulated in packets where the work of packetizing and de-packetizing data and status-message traffic is handled by the transaction layer of the PCIe port.